In the manufacture of tobacco products, efforts at dilution, i.e., controlled introduction of air in the course of smoking, have looked to perforating the tobacco wrapper and to perforating the filter or plug tipping paper. Since the filter tipping paper is of substantially less area than the tobacco wrapper and portions of such area are not usefully perforatable by reason of being engaged by the smoker or adhesive-coated, the perforated area per unit length of useful area need be increased to attain desired dilution levels. Offsetting considerations apply here, however, since, as hole area per perforation is increased, subdued hole visibility lessens and smoke issuance through the tipping paper during non-puffing periods increases. An adequate compromise is to increase the density of holes of individual size sufficiently small to render the tipping paper apparently unperforated and substantially non-smoke issuing.
For relatively high dilution levels of interest, and considering tipping paper area usable for perforating, applicants concluded that holes in size ranging from ten to one hundred microns in diameter and spaced mutually by less than one millimeter are required. On examining filter tipping papers perforated by commercial suppliers at sufficient porosity (i.e., in perforated area), applicants found the products either insufficient in hole density or not available in production volume. While applicants have no knowledge as to the details of methods by which such examined filter tipping papers were made, it was evident from hole characteristics and density that the papers were electrically perforated. In respect of one sample paper found to have sufficient hole density, subsequently received production samples thereof evidenced substantially less hole density, leading to the conclusion that the sample paper was laboratory-tailored and not reproducible in production volume.
Concerning electrical perforation of webs, a vast number of prior efforts are known, as set forth in the prior art statement under 37 C.F.R. 1.97 and 1.98, to be filed herein.